To sync NTP that is out of the clock for more than the panic threshold e.g. if the time is substantially off, you either call ntpd with the
-g Normally, ntpd exits with a message to the system log if the offset exceeds the panic threshold, which is 1000 s by default. This option
allows the time to be set to any value without restriction; however,
this can happen only once. If the threshold is exceeded after that,
ntpd will exit with a message to the system log. This option can be
used with the -q and -x options.
And you put in
tinker panic 0
By default, the NTP daemon sometimes panics and exits if the
underlying clock appears to be behaving erratically. This option
causes the daemon to keep running instead of panicking.
tinker panic 0 is specially useful for VMs, whether recovering a snapshot, or a VM with a misbehaving clock.
As a pertinent note,
tinker panic 0 should be the first line of the configuration file.